#include <stdio.h>
#define _STDC_LIB_EXT1_ 1
#include <string.h>

int main (void)
{
    #if defined _STDC_LIB_EXT1_
        printf("OK!!\n");
    #else
        printf("NO!!\n");
    #endif

    char str1[50] = "To be, or not to be, ";
        char str2[] = "that is the question.";
    int retval = strcat_s(str1, sizeof(str1), str2);
    if(retval)
        printf("There was an error joining the strings. Error code = %d\n", retval);
    else
        printf("The combined strings:\n%s\n", str1);

return 0;
}

语句：int retval = strcat_s(str1, sizeof(str1), str2);是将strcat_s()函数的返回值给 retval吗？然后用if判断。

1天了，为啥没人回啊。我觉得retval就是strcat_s（）函数的返回值，然后就用if测试，判断是否返回值正确。但是为何retval要声明为int型？ 不是size_t型吗？